1. Field of the Invention
This invention relates to an airtight container assembly which prevents bacterial contamination caused by "slow-leak", i.e., unwanted bacteria slowly enter the interior of the container assembly through small gaps between a sealing member and a mouth portion of the container assembly when the seal between the seal member and the mouth portion is inferior. In particular, this invention relates to a container assembly provided with an antibacterial agent for preserving the contents of the container assembly even when slow-leak occurs.
2. Background of the Art
Heretofore, in order to aseptically pack a beverage such as a juice, juice drink, coffee, tea, milk drink, drinking water, and other non-carbonated soft drinks in a container assembly, hot-packing is conducted. For example, by heating to a temperature of 82.degree. to 85.degree. C. for fruit drink, 85.degree. C. to 90.degree. C. for coffee or tea, and 70.degree. C. to 75.degree. C. for mineral water, sterilization of the contents and the interior of the container assembly is conducted. After hot-packing of the contents in the container assembly, the container assembly is capped immediately, and then normally subjected to overturning-sterilization, in which the container assembly is overturned so as to sterilize the neck portion of the container assembly. In the above processes, capping is conducted when the temperature of the contents is high, i.e., the air present inside the container assembly is expanded, and thus, as the contents cool, the pressure of the interior of the container assembly is reduced because the cap liner and the rim of the mouth portion are airtightly sealed. However, when the airtight seal between the cap liner and the rim of the mouth portion is inferior, although no liquid leaks, the outside air containing unwanted bacteria enters the interior of the container assembly through small gaps therebetween, i.e., "slow-leak" occurs. Slow-leak may occur in situations other than in hot-packing. For example, during storage of container assemblies, due to a change in volume of the contents corresponding to a change in surrounding temperature, the outside air containing unwanted bacteria tends to enter the interior of the container assemblies.
When slow-leak occurs, not only air but also various bacteria and eumycetes enter the interior and cause the contents to deteriorate. Since slow-leak occurs very slowly, it is extremely difficult to detect occurrence. Once it is detected, all of the products produced in the same line or in the same lot as that of the detected product often must be abandoned because tracing slow-leak is time-consuming and unfeasible. This is a very serious and costly problem. Causes of slow-leak may be slight scratches on the rim of the mouth portion of a container assembly, or bruising a cap. These defects render the seal between the cap liner and the rim of the mouth insufficient. There is no significant solution to fully eliminate such defects, and in general, one per ten thousand to one million container assemblies is consistently identified as a slow-leak container assembly.
As described above, causes of slow-leak may be (a) a small gap between the cap liner and the rim of the mouth portion due to scratches on the surface of the rim; (b) a bruise caused during transportation of container assemblies, i.e., an edge of the cap is bumped; and (c) a seal defected caused by defective capping operation. In any case, small gaps are unavoidably formed through which not only outside air but also unwanted bacteria enter the interior of container assemblies, as the inside pressure is lower than that of the outside, resulting in contaminated contents.